Substrate with optical waveguide and method of making the same

ABSTRACT

A substrate with an optical waveguide includes a substrate having a through hole and two sides, a first optical waveguide defined in the though hole of the substrate so as to linearly extend between both sides of the substrate, a second optical waveguide defined on at least one of the sides of the substrate, and direction changing means for changing a transmitting direction of a light signal from either one of the first and second optical waveguides to the other. Each optical waveguide includes a core layer for transmitting the light signals and a clad layer formed around the core layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a substrate provided with an optical waveguidethrough which a light signal is transmitted and a method of making sucha substrate.

2. Description of the Related Art

A substrate with an optical waveguide has recently been proposed whichis provided with an optical waveguide so that light signals and electricsignals are simultaneously treated. For example, the prior art hasproposed a construction in which an optical waveguide is provided on oneof two sides of a substrate and a reflecting face serving as directionchanging means and a light-sensitive element are disposed at one endside of the optical waveguide. In this construction, a light signalintroduced into the optical waveguide is reflected on the reflectingface so that the direction of the light signal is changed to thelight-sensitive element side. The light signal is then sensed by thelight-sensitive element.

In the above-described construction, however, it is only at one side ofthe substrate that the light signal is transmitted. In other words, thetransmitting direction of the light signal can be changed onlytwo-dimensionally or on a plane. As a result, a region used for thelight signal transmission is limited in a single substrate.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a substratewith an optical waveguide in which the substrate can be effectively usedfor the light signal transmission and which can cope withhigh-densification of the substrate.

Another object of the invention is to provide a method of making asubstrate with an optical waveguide in which the optical waveguide canbe desirably made in the substrate.

The present invention provides a substrate with an optical waveguidecomprising a substrate having a through hole and two sides, a firstoptical waveguide defined in the through hole of the substrate so as tolinearly extend between both sides of the substrate, a second opticalwaveguide defined on at least one of the sides of the substrate, anddirection changing means for changing a transmitting direction of alight signal from either one of the first and second optical waveguidesto the other, each optical waveguide including a core layer fortransmitting the light signals and a clad layer formed around the corelayer.

According to the above-described substrate, the first optical waveguidecan optically connect between both sides of the substrate. Consequently,since the optical waveguides through which the light signal istransmitted are provided on both sides of the substrate respectively,the substrate can be used effectively. Further, the first opticalwaveguide is defined in the through hole of the substrate. Consequently,the light signal can be transmitted from one side to the other side atany location of the substrate and accordingly, a transmission pattern ofthe light signal can be designed more freely.

In this construction, the transmitting efficiency of the light signalcan further be improved. Further, two second optical waveguides arepreferably defined at both sides of the substrate respectively.Additionally, the substrate is preferably made of polyimide.

In another preferred form, the substrate further comprises signalconverting means provided on said other side of the substrate forconverting the light signal received via the first optical waveguide toa corresponding electric signal, and an electric circuit section intowhich the electric signal is supplied. According to this construction,the light signal transmitted via, for example, an external optical fibernetwork is received at said one side of the substrate and furthertransmitted via the first optical waveguide to said other side of thesubstrate, where the light signal is converted to the electric signal bythe signal converting means. When the electric signal is thereaftersupplied to an electric or electronic circuit, the light signal can beused so that information is transmitted at high speeds or over a wideband between electric circuit sections of respective substratesconnected together via the network.

The invention also provides a method of making a substrate with anoptical waveguide, the substrate having a through hole and two sides andcomprising a first optical waveguide defined in the through hole of thesubstrate so as to linearly extend between both sides of the substrate,a second optical waveguide defined on at least one of the sides of thesubstrate, and direction changing means for changing a transmittingdirection of a light signal from either one of the first and secondoptical waveguides to the other. The method comprises the steps ofimmersing the substrate in a resin liquid for making the first opticalwaveguide so that the through hole is filled with the resin liquid, andhardening the resin liquid after the immersing step, thereby making thefirst optical waveguide.

According to the above-described method, the first optical waveguide canbe made desirably and readily.

The invention further provides a method of making a substrate with anoptical waveguide, the substrate having a through hole and two sides andcomprising a first optical waveguide including a core layer linearlyformed between both sides of the substrate for propagating a lightsignal and a clad layer covering the core layer, a second opticalwaveguide defined on at least one of the sides of the substrate, anddirection changing means for changing a transmitting direction of alight signal from either one of the first and second optical waveguidesto the other. The method comprises the steps of disposing a metal diehaving one open end at the substrate side along a route of the secondoptical waveguide so that the other end of the die covers an opening ofthe through hole, and filling the die with a resin liquid for formingthe optical waveguides, and hardening the resin liquid subsequently tothe filling step, thereby forming the first and second opticalwaveguides.

According to the above-described method, the first and second opticalwaveguides are simultaneously formed by using the metal die.Consequently, steps of manufacturing the substrate can be simplified.Further, since the first and second optical waveguides are integrallyformed, no boundary between them is formed. Consequently, a reflectionloss resulting from transmission of the light signal between bothwaveguides can be reduced to a large extent.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome clear upon reviewing the following description of the preferredembodiments, made with reference to the accompanying drawings, in which:

FIG. 1 is a partial longitudinal section of a substrate with an opticalwaveguide of a first embodiment in accordance with the presentinvention;

FIG. 2 is a partial broken perspective view of the substrate;

FIGS. 3A to 3D illustrate steps of forming a first optical waveguide inthe substrate;

FIG. 4 is a perspective view of the substrate with first and secondoptical waveguides;

FIG. 5 is a view similar to FIG. 2, showing a substrate of a secondembodiment in accordance with the present invention;

FIG. 6 is a view similar to FIG. 1, showing a substrate of a thirdembodiment in accordance with the present invention;

FIG. 7 is a view similar to FIG. 1, showing a substrate of a fourthembodiment in accordance with the present invention; and

FIG. 8 is a view similar to FIG. 1, showing a substrate of a fifthembodiment in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described withreference to FIGS. 1 to 4. A substrate 1 is made from a polyimide filmhaving a high heat resistance. The polyimide film has a thickness of 125μm and a refractive index of 1.751. The film has elasticity. Thesubstrate 1 is provided with a first optical waveguide 2 extendingbetween upper and lower sides thereof in the direction of the thicknessthereof, as viewed in FIG. 1. The first optical waveguide 2 is definedin a through hole 3 formed through the substrate 1. The first opticalwaveguide 2 includes a core layer 4 for transmitting a light signal anda clad layer 5 formed around the core layer 4. The core layer 4 is madeof, for example, a fluorine-contained polyimide resin having arefractive index of 1.560. The clad layer 5 is made from, for example, afluorine-contained polyimide resin having a refractive index of 1.541.

A method of forming the first optical waveguide 2 in the substrate 1will now be described with reference to FIGS. 3A to 3D.

1. A circular through hole 3 is formed in a portion of the substrate 1made from the polyimide film, in which portion the first opticalwaveguide 2 is to be formed. See FIG. 3A. This through hole 3 is formedby a KrF excimer laser with a wavelength of 248 nm. The through hole 3has an inner diameter of, for example, 150 μm.

2. The substrate 1 is then immersed in a first resin from which the cladlayer 5 is made or a fluorine-contained polyimide resin liquid (dipping)so that the through hole 3 is filled with the first resin. In this case,the first resin also adheres to both sides of the substrate 1. Then,after the substrate 1 is taken out of the resin liquid, the first resin5 a is hardened. See FIG. 33. The through hole 3 is buried with thefirst resin 5 a as the result of hardening.

3. A circular core through hole 6 (see FIG. 3C) is formed by a laser orplasma in the through hole 3 buried with the first resin 5 a with theclad layer S remaining. The core through hole 6 has an inner diameterof, for example, 125 μm. The core through hole 6 may be formed byinserting a generally bar-shaped hollow member.

4. The substrate 1 formed with the core through hole 6 is immersed in asecond resin from which the core layer 4 is made or more specificallyfluorine-contained polyimide resin, so that the core through hole 6 isfilled with the second resin. In this case, the second resin alsoadheres to both sides of the substrate 1. Then, after the substrate 1 istaken out of the resin liquid, the second resin 4 a is hardened. SeeFIG. 3D. The core through hole 6 is buried with the first resin 5 a asthe result of hardening. As a result, the core layer 4 is made of thesecond resin 4 a in the through hole 3 of the substrate 1, and the cladlayer 5 is made of the first resin 5 a.

Two second optical waveguides 7 each having the same construction areprovided on an upper side and an underside of the substrate 2 formedwith the fist optical waveguide 2 respectively as shown in FIGS. 1 and2. Each second optical waveguide 7 is made from a fluorine-containedpolyimide resin having a refractive index of 1.57, for example. Thesecond optical waveguides 7 have reflecting faces 8 formed to face bothends of the first optical waveguide 2 respectively. Each reflecting face8 constitutes direction changing means for changing a direction of thelight signal. The reflecting faces 8 are inclined at an angle of 45degrees relative to the upper side and the underside of the substrate 1respectively. A metal thin film 8 a is preferably formed on eachreflecting face 8, so that a reflectance of each reflecting face can beimproved. The thin film 8 a is eliminated in FIG. 2.

The second optical waveguides 7 are previously formed independently ofthe substrate 1. More specifically, the second optical waveguides 7 arefixedly bonded on the upper side and the underside of the substrate 1 bythe second resin 4 a provided for forming the core layer 4 and servingas an bonding agent. The second optical waveguides 7 are disposed sothat their lengths in which the light signal passes through them aresubstantially perpendicular to each other.

When the light signal is supplied to the upper second optical waveguide7 in the direction of arrow A in FIGS. 1 and 2, for example, the lightsignal passes through the second optical waveguide 7, impinging on thereflecting face 8 a. As a result, the direction of the light signal ischanged to the first optical waveguide 2 side. The light signal thenpasses through the core layer 4 of the first optical waveguide 2downward. The light signal then impinges on the reflecting face 8 a ofthe lower second optical waveguide 7 such that its direction is changed.The light signal then passes through the lower second optical waveguide7 to thereby be delivered. The input light signal supplied to the uppersecond optical waveguide 7 has a direction differing by 90 degrees froma direction of the output light signal delivered from the lower secondoptical waveguide 7. On the other hand, when supplied to the loweroptical waveguide 7, the light signal is delivered from the upper secondoptical waveguide 7 through a reverse path with respect to theabove-described one.

Referring now to FIG. 4, a plurality of sets of the first and secondoptical waveguides 2 and 7 are provided on a single substrate 1. In thisconstruction, too, the upper and lower second optical waveguides 7 ineach set are disposed so that their directions of length in which thelight signal passes through them are substantially perpendicular to eachother. Further, a photosensitive element may be provided on theunderside of the substrate 1, instead of the lower second opticalwaveguide 7 although this is not shown in the drawings. in thisconstruction, the light signal supplied to the upper second opticalwaveguide 7 can be detected via the first optical waveguide 2 by thephotosensitive element.

According to the above-described embodiment, the first optical waveguide2 is disposed in the substrate 1 so as to extend in the direction ofthickness of the substrate, so that the upper side and the underside ofthe substrate 1 can optically be connected to each other. Consequently,since means for treating the light signal can be provided on both sidesof the substrate 1, the substrate can effectively be used and thehigh-densification of the substrate can be coped with.

Further, the first optical waveguide 2 is provided in the through hole 3formed in any location of the substrate 1. The substrate 1 can becompacted even though the first optical waveguide 2 is provided in thesubstrate 1. Additionally, a transmission pattern of the light signalcan be designed more freely. Further, the first optical waveguide 2 isformed into a linear shape. When both second optical waveguides 7 arecoupled together, they are mounted so that the reflecting faces 8 agreewith the location of the core layer 4 formed in the core through hole 6.Consequently, the coupling can readily be carried out.

Further, the first optical waveguide 2 includes the core layer 4 fortransmitting the light signal and the clad layer 5 formed around thecore layer 4. This improves the transmission efficiency of the firstoptical waveguide 2, whereupon the light signal can desirably betransmitted. Additionally, the second optical waveguides 7 are providedon the upper side and the underside of the substrate 2 respectively. Thedirections of the upper and lower second optical waveguides 7 aresuitably set so that the direction of the light signal can freely be setin the substrate 1.

Further, when the first optical waveguide 2 is formed in the substrate1, the manufacturing process including the above-described steps 1 to 4is employed. Consequently, the first optical waveguide 2 can be formedin the substrate 1 desirably and readily.

FIG. 5 illustrates a second embodiment of the invention. The secondembodiment differs from the previous embodiment in the following point.The lower second optical waveguide 7 longitudinally extends in the samedirection as the upper second optical waveguide 7 extends.

FIG. 6 illustrates a third embodiment of the invention. The thirdembodiment differs from the first embodiment in the following point. Thefirst optical waveguide 10 is provided at the center of the through hole3 formed in the substrate 1 and includes a central core layer 11 and aclad layer 12 provided around the core layer 11. Second clad layers 13are provided on the upper side and the underside of the substrate 1 andaround the clad layer 12 in the through hole 3.

A second optical waveguide 14 provided on the upper side of thesubstrate 1 includes a central core layer 15 and a clad layer 16disposed around the core layer 15. The second optical waveguide 14 hasan end on which the reflecting face 8 is formed. The direction of thecore layer 15 of the second optical waveguide 14 is changed at thereflecting face 8 so that the core layer 15 and the core layer 11 of thefirst optical waveguide 10 are connected together. On the underside ofthe substrate 1 are provided an optical waveguide similar to that on theupper side of the substrate 1, a photosensitive element and a photodiode17 as shown in FIG. 7.

According to the third embodiment, the upper side and the underside ofthe substrate 1 can optically be connected to each other, whereupon thelight signal can be transmitted between the upper side and the undersideof the substrate 1. Consequently, the substrate 1 can effectively beused for transmission of the light signal. This construction can copewith high-densification of components mounted on the substrate 1.

FIG. 7 illustrates a fourth embodiment of the invention. The fourthembodiment differs from the first embodiment in the following point. Aphotodiode 17 serving as the signal converting means is provided beneaththe core through hole 6 on the underside of the substrate 1, instead ofthe second optical waveguide 7. The photodiode 17 includes a lead wire17 a serving as a terminal from which the photodiode delivers anelectric signal. The lead wire 17 a is electrically connected bysoldering to one end of a wiring pattern 18 made of copper foil on theunderside of the substrate 1.

An LSI (electric circuit section) 19 comprising a microcomputer isdisposed on the left of the photodiode 17 as viewed in FIG. 7. The LSI19 includes a lead wire 19 a serving as an input terminal andelectrically connected to the other end of the wiring pattern 18. Theelectric circuit section includes an electric circuit provided with anelectronic circuit throughout the description.

The operation of the substrate of the fourth embodiment will now bedescribed. Assume now an external optical communication networkcomprising an optical fiber, although this is not shown in the drawingsThe upper second optical waveguide 7 is connected to the opticalcommunication network or coupled to the optical fiber of the network.The substrate 1 is installed in a dwelling or an office to serve as aterminal of the network. A light signal transmitted from a distantsignal transmission point or node is supplied via the opticalcommunication network to the second optical waveguide 7.

The light signal supplied to the second optical waveguide 7 is suppliedvia the first optical waveguide 2 to the photodiode 17, so that thelight signal is converted to an electric signal. The electric signal isthen supplied to the LSI 19. Accordingly, when the LSI 19 constitutes apart of a personal computer used at a home, high-speed and wide-banddata transmission by means of a light signal can be realized among alarge number of personal computers.

FIG. 8 illustrates a fifth embodiment of the invention. The fifthembodiment differs from the first embodiment in the following. In thefifth embodiment, two metal dies are attached to opposite sides of thesubstrate 1 which has passed through the steps of FIGS. 3A to 3C in thefirst embodiment, respectively. A resin liquid 21 is injected into aspace defined by the substrate and the metal dies 20 so that first andsecond optical waveguides 22 and 23 are formed en bloc.

Each die 20 has a shape conforming to that of the second opticalwaveguide 23. More specifically, each die 20 is formed substantiallyinto the shape of a rectangular box and is open at the substrate 1 side,a resin-liquid injecting side and a resin-liquid sucking side. The dies20 have inclined faces 20 a at portions opposed to the injecting andsucking openings respectively. Each inclined face is at an angle of 45degrees relative to the substrate 1. The dies 20 are disposed so thatportions thereof having the inclined faces 20 a cover upper and loweropenings of the core through hole 6 respectively.

A suction unit 24 such as a vacuum pump is connected to the open end ofthe die 20 disposed at the underside of the substrate 1. An injector forinjecting the resin liquid 21 is mounted on the open end of the die 20disposed at the upper side of the substrate 1. The resin liquid 21 offluorine-contained polyimide is injected from the injector into a spacedefined by the dies 20 and the substrate 1. The injected resin liquid 21is sucked into the space by the suction unit 24. When the space iscompletely filled with the resin liquid 21, the substrate 1 and the dies20 are retained in their states so that the resin liquid 21 is hardened.After the resin liquid 21 has been hardened, the dies 20 are removed andthe first and second optical waveguides 22 and 23 are formed en bloc.

According to the above-described fifth embodiment, the metal dies 20 aredisposed at both sides of the substrate 1 respectively, and the resinliquid 21 is injected into the space defined by the dies 20 and thesubstrate 1 so that the first optical waveguide 22 and the secondoptical waveguides 23 are formed en bloc. Consequently, themanufacturing process can be simplified. Furthermore, no boundary faceor interface (discontinuous face) is structurally provided between thefirst optical waveguide 22 and each second optical waveguide 23. Thefifth embodiment differs from the first embodiment in this point.Consequently, a reflection loss resulting from transmission of lightsignal between the optical waveguides 22 and 23 can be reduced to alarge extent. Further, since the inclined faces 20 a are formed at endsides of the metal dies 20 respectively, the optical waveguides 22 and23 and the direction changing means are simultaneously formed, themanufacturing process can further be simplified.

Additionally, the resin liquid 21 is injected from the side of the metaldie 20 disposed at the upper side of substrate 1 and sucked by thesuction device 24 disposed at the underside of the substrate 1, so thatthe space defined by the substrate 1 and the dies 20 is completelyfilled with the resin liquid 21 without void. Further, the resin liquidcan also be injected when the substrate 1 is maintained in a horizontalstate.

The first optical waveguide 2 or 10 may be formed by only the core layer4 or 11. A previously formed discrete first optical waveguide 2 or 10may be inserted into the through hole 3 of the substrate 1 depending onthe thickness of the substrate. A groove may be formed in one side ofthe substrate so that the second optical waveguide 7 or 14 is providedtherein. The thin film 8 a may or may not be provided.

The electric circuit section should not be limited to the LSI 19. It maycomprise a simpler circuit arrangement. For example, the electriccircuit section may receive an externally transmitted signal so that anoutput result according to the received signal is obtained at thesubstrate 1 side. More specifically, an LED may be turned on or off.

In the fifth embodiment, the metal dies 20 may not be disposed at bothsides of the substrate 1 when the first and second optical waveguides 22and 23 are formed with the dies 20. For example, when the photodiode 17is disposed on the underside of the substrate 1 as in the fourthembodiment, only one metal die 20 may be disposed at the upper side ofthe substrate 1 and the underside opening may be closed by a suitableclosing member. Further, only one second optical waveguide 23 may beformed on the upper side of the substrate 1.

Further in the fifth embodiment, the dies 20 may be disposed on thesubstrate 1 in the state shown in FIG. 3A without forming the clad layer5 so that an optical waveguide having only a core layer is formed. Eachdie 20 may not be provided with the inclined face 20 a. For example, theend corresponding to the inclined face may be formed into the shape of asquare pole, and the square end may be cut with cutting means such as aknife when the resin liquid is hardened and the dies 20 are removed, sothat the 45-degree inclined face may be formed.

The foregoing description and drawings are merely illustrative of theprinciples of the present invention and are not to be construed in alimiting sense. Various changes and modifications will become apparentto those of ordinary skill in the art. All such changes andmodifications are seen to fall within the scope of the invention asdefined by the appended claims.

We claim:
 1. A substrate with an optical waveguide comprising: asubstrate having a through hole and two sides; a first optical waveguidedefined in the through hole of the substrate so as to linearly extendbetween both sides of the substrate; a second optical waveguide definedon at least one of the sides of the substrate; and direction changingmeans for changing a transmitting direction of a light signal fromeither one of the first and second optical waveguides to the other, eachoptical waveguide including a core layer for transmitting the lightsignals and a clad layer formed around the core layer.
 2. A substrateaccording to claim 1, wherein two second optical waveguides are definedat both sides of the substrate respectively.
 3. A substrate according toclaim 1, wherein the substrate is made of polyimide.
 4. A substrateaccording to claim 1, wherein the second optical waveguide has one endlocated at the though hole side and the direction changing means isformed as an inclined face formed on the end of the second opticalwaveguide at an angle of 45 degrees relative to the substrate.
 5. Asubstrate according to claim 4, wherein the direction changing meansincludes a metal thin film formed on the inclined face.
 6. A substrateaccording to claim 1, further comprising signal converting meansprovided on said other side of the substrate for converting the lightsignal received via the first optical waveguide to a correspondingelectric signal, and an electric circuit section into which the electricsignal is supplied.
 7. A method of making a substrate with an opticalwaveguide, the substrate having a through hole and two sides andcomprising a first optical waveguide including a core layer linearlyformed between both sides of the substrate for propagating a lightsignal and a clad layer covering the core layer, a second opticalwaveguide defined on at least one of the sides of the substrate, anddirection changing means for changing a transmitting direction of alight signal from either one of the first and second optical waveguidesto the other, the method comprising the Steps of: immersing thesubstrate formed with the through hole in a first resin liquid formaking the clad layer so that the through hole is filled with the resinliquid and thereafter hardening the resin liquid; forming a core throughhole in the through hole filled with the resin liquid with the cladlayer remaining; disposing a metal die having one open end at thesubstrate side along a route of the second optical waveguide so that theother end of the die covers an opening of the through hole, and fillingthe die with a resin liquid for forming the optical waveguides; andhardening the resin liquid subsequently to the filling step, therebyforming the first and second optical waveguides.
 8. A method of making asubstrate with an optical waveguide, the substrate having a through holeand two sides and comprising a first optical waveguide defined in thethrough hole of the substrate so as to linearly extend between bothsides of the substrate, a second optical waveguide defined on at leastone of the sides of the substrate, and direction changing means forchanging a transmitting direction of a light signal from either one ofthe first and second optical waveguides to the other, the methodcomprising the steps of: immersing the substrate in a resin liquid formaking the first optical waveguide so that the through hole is filledwith the resin liquid; and hardening the resin liquid after theimmersing step, thereby making the first optical waveguide.
 9. A methodaccording to claim 8, wherein two second optical waveguides are definedat both sides of the substrate respectively.
 10. A method according toclaim 8, wherein the substrate is made of polyimide.
 11. A methodaccording to claim 8, wherein the second optical waveguide has one endlocated at the though hole side and the direction changing means isformed as an inclined face formed on the end of the second opticalwaveguide at an angle of 45 degrees relative to the substrate.
 12. Amethod according to claim 11, wherein the direction changing meansincludes a metal thin film formed on the inclined face.
 13. A methodaccording to claim 8, further comprising signal converting meansprovided on said other side of the substrate for converting the lightsignal received via the first optical waveguide to a correspondingelectric signal, and an electric circuit section into which the electricsignal is supplied.
 14. A method of making a substrate with an opticalwaveguide, the substrate having a through hole and two sides andcomprising a first optical waveguide including a core layer linearlyformed between both sides of the substrate for propagating a lightsignal and a clad layer covering the core layer, a second opticalwaveguide defined on at least one of the sides of the substrate, anddirection changing means for changing a transmitting direction of alight signal from either one of the first and second optical waveguidesto the other, the method comprising the steps of: immersing thesubstrate formed with the through hole in a first resin liquid formaking the clad layer so that the through hole is filled with the resinliquid and thereafter hardening the resin liquid; forming a core throughhole in the through hole filled with the resin liquid with the cladlayer remaining; and immersing the substrate formed with the corethrough hole in a second resin liquid for making a core layer so thatthe through hole is filled with the second resin liquid and hardeningthe second resin liquid after the second resin liquid immersing step,thereby making the first optical waveguide.
 15. A method of making asubstrate with an optical waveguide, the substrate having a through holeand two sides and comprising a first optical waveguide including a corelayer linearly formed between both sides of the substrate forpropagating a light signal and a clad layer covering the core layer, asecond optical waveguide defined on at least one of the sides of thesubstrate, and direction changing means for changing a transmittingdirection of a light signal from either one of the first and secondoptical waveguides to the other, the method comprising the steps of:disposing a metal die having one open end at the substrate side along aroute of the second optical waveguide so that the other end of the diecovers an opening of the through hole, and filling the die with a resinliquid for forming the optical waveguides; and hardening the resinliquid subsequently to the filling step, thereby forming the first andsecond optical waveguides.
 16. A method according to claim 15, whereinthe die has at said one end side thereof an inclined face formed at anangle of 45 degrees relative to the substrate.
 17. A method according toclaim 15, wherein the die is disposed at both sides of the substrate soas to sandwich the through hole.
 18. A method according to claim 17,wherein the resin liquid is poured into the die from a portion of thedie disposed at one side of the substrate and sucked from a portion ofthe die disposed at the other side of the substrate.